The present invention relates to a flexible drive coupling and in particular to a drive coupling having improved means for securing the coupling to a shaft.
Flexible drive couplings of the present type are typically used to connect the driving shaft of a prime mover, such as a motor or engine, to the driven shaft of a load such as a pump or other machine. The drive coupling is installed by securing one coupling member to the shaft of the prime mover and the other coupling member to the shaft of the load, and then aligning the two shafts so that the two coupling members mate with one another. Drive couplings of the present type typically include a flexible coupling insert that is located intermediate the two main coupling members and serves to transmit the torque from the coupling member fastened to the prime mover to the coupling member fastened to the load. The coupling insert also serves to accept the strain caused by any misalignment of the two shafts, thus avoiding excessive strain on the bearings of the prime mover and load.
Presently, there are two principal known methods of securing a coupling member to a shaft. The first method involves the use of a simple set screw that is typically located over the keyway insert in the central bore of the coupling, and is adapted to be securely tightened against the key insert when the coupling is properly positioned at the end of the shaft. The set screw can also be utilized with splined shaft couplings as well. The other principal type of securing means utilized is the clamp-type coupling. The clamp-type coupling has a narrow gap in one section of the coupling member that is bridged by a set screw threadedly engaged in a hole formed through the coupling member perpendicular to the gap. The coupling member is thus secured to the shaft by tightening the set screw to thereby close the gap and clamp the coupling member to the shaft.
These conventional fastening means do not, however, work well with certain types of flexible shaft couplings, and in particular, with those made of non-metallic material such as plastic. Specifically, when a set screw is utilized, the plastic female threads in the coupling are easily stripped, especially after repeated installations. Moreover, the formation of the transverse hole required in the clamp-type coupling tends to significantly reduce the integrity of the coupling member around the area of the hole. Consequently, the stress limits of the coupling member are severely restricted.
Accordingly, it is the primary purpose of the present invention to provide an improved means of fastening a flexible drive coupling to a shaft in a manner which will not reduce the integrity of the coupling. Although the present invention has particular application to non-metalic drive couplings, the concepts of the present invention are equally applicable to standard metal couplings as well. In general, the coupling members of a flexible drive coupling according to the present invention have a central bore form therein that is substantially epitrochoidal in shape. An insert having a corresponding shape is fitted within the bore of each coupling member. The insert has a shaft bore formed therein and a gap in one side thereof generally intermediate the apexes of the insert. Due to the shape of the insert, the coupling member is automatically secured to a shaft upon the application of torque to the insert. In particular, as the insert attempts to rotate within the outer coupling member, the gap in the insert is closed thereby adapting the bore in the insert to the size of the shaft. Moreover, it will be appreciated that the coupling member will remain secured to the shaft while the shaft is rotating due to the continuous application of torque to the insert from the shaft or the outer coupling member, depending upon whether the coupling member is fastened to the driving or driven shaft, respectively.
Thus, it can be seen that a novel flexible drive coupling is provided that is exceptionally easy to install. Moreover, it will be appreciated that, due to the presence of the removable insert, a single coupling can accommodate various sized shafts simply by changing the insert. In addition, the flexible drive coupling according to the present invention provides several manufacturing advantages over prior art type couplings. In particular, with the known clamp-type coupling discussed above, the shaft bore must be manufactured to extremely close tolerances in order to provide a coupling member that can initially be "push-fitted" onto the shaft and subsequently clamped tightly to the shaft by the relative small reduction in diameter of the central bore as the gap is closed by the tightening of the transverse set screw. With the present structure, however, the epitrochoidal insert is a relatively thin-walled structure which more readily adapts to the size of the shaft. Therefore, the tolerance of the shaft bore in the insert is not as critical. Accordingly, the present flexible drive coupling provides the advantages of a clamp-type coupling in that positive retention and centering of the coupling on the shaft is assured, without the associated manufacturing disadvantages of the clamp-type coupling.
Additional objects and advantages of the present invention will become apparent from a reading of the detailed description of the preferred embodiment which makes reference to the following set of drawings in which :